1. Field of the Invention
The present invention relates generally to a device and method for attaching to bones.
2. Description of Related Art
Broken bones, such as compression fractures of one or more vertebrae in the spine, may be treated with internal fixation. Any indication needed spinal stability can also be treated by internal fixation. Examples include scoliosis, kyphosis, spondylothisthesis and rotation, segmental instability, such as disc degeneration and fracture caused by disease and trauma and congenital defects, and degeneration caused by tumors.
As shown by FIG. 1, internal fixation in the spine is often accomplished by first screwing fixation screws 200 into the pedicles and vertebral bodies of the vertebrae 88. FIG. 2 shows that the fixation screws 200 are then typically attached to a rigid fixation rod or plate 94 that provides support between one or more weakened vertebra 88. This support often immobilizes the vertebra 88 to which the fixation screws 200 have been inserted.
FIG. 3 illustrates that existing fixation systems often have the fixation rod or plate 94, through which a number of fixation screws 200 are deployed. The screw head 202 prevents the fixation rod 88 from separating from the fixation screw 200. The fixation screw 200 also has a screw body 204 which has a screw longitudinal axis 206 often static relative to the fixation rod 94.
FIG. 4 illustrates that in some existing fixation systems, the fixation screws 200 can be polyaxial screws: attached to the fixation rod or plate 94 in a manner so that the screw longitudinal axis 206 can rotate, as shown by arrows, with respect to the fixation rod 94.
Backing out or loosening of the fixation screws can cause a reduction of the fixation, up to complete failure or even resulting in additional complications.
Furthermore, the bones are often weak and under heavy loads, the bones can fail and the fixation screws can be ripped from the bone resulting in complete failure and additional damage to the bone.
Therefore, a fixation screw that can substantially eliminate the risk of backout, and can provide a higher anchoring force is desired. A fixation screw that can also minimize bone failure is desired.